Generating leakage canceling current in electric vehicle charging systems

ABSTRACT

A system includes a power source, a power converter, a leakage current cancelation circuit, a load, and a ground node. The power converter is coupled to the power source and supplies the load. During operation of the power converter, a common mode current flows from the load to the ground node via a leakage capacitance. The leakage current cancelation circuit receives at least one signal indicative of the common mode current and generates a leakage cancelation current that is injected into at least one node of the system. The leakage cancelation current has a magnitude opposite a magnitude of the common mode current. For example, the leakage current cancelation circuit receives supply voltage signals output by the power converter, and generates and supplies the leakage cancelation current onto input nodes of the power converter such that a current level on the ground node is between −3.0 milliamperes and +3.0 milliamperes.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119 of provisionalapplication Ser. No. 62/042,696, entitled “Generating Leakage CancelingCurrent In Electric Vehicle Charging Station System,” filed Aug. 27,2014. The subject matter of provisional application Ser. No. 62/042,696is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to power systems involvingpower converters, and more specifically to methods for charging electricvehicles.

BACKGROUND INFORMATION

An electric vehicle typically includes energy storage systems that storeelectrical energy, such as battery packs. Power circuitry within theelectric vehicle uses energy stored in the battery packs to drive anelectric motor of the electric vehicle. After the energy stored in thebattery packs has been depleted, the battery packs must be charged. Anelectric vehicle charge station couples the power circuitry of theelectric vehicle to an Alternating Current (AC) power source to chargethe battery packs.

Electric vehicle charging stations usually must comply with safetyregulations and standards because of the hazardous voltage and currentlevels available at the AC power source to the power circuitry of theelectric vehicle. UL 2231 defines standards for electric vehiclecharging stations and for protection devices in the charging stations.One type of protection device commonly found in a charging station is aGround Fault Interrupter (GFI) circuit. If the GFI circuit detectsimbalanced current on the charging conductors, then the GFI circuitdisables the charging station and the electric vehicle battery packsstop charging. This requirement limits the common mode capacitance ofvehicle circuits to a low value, which can be difficult to achieve forsome vehicle designs.

SUMMARY

A system includes a power source, a power converter, a leakage currentcancelation circuit, a load, and a ground node. The power converter iscoupled to the power source and supplies the load. During operation ofthe power converter, a common mode current flows from the load to theground node via a common mode capacitance. The common mode current isalso referred to as a “leakage current”, and the common mode capacitanceis also referred to as a “leakage capacitance”. Under certainconditions, the leakage current that flows on the ground node isundesirable. To mitigate these undesirable effects, the leakage currentcancelation circuit generates a leakage cancelation current. The leakagecancelation current has a magnitude opposite the leakage current suchthat an instantaneous sum of the leakage cancelation current and theleakage current is substantially near zero.

To generate the leakage cancelation current, the leakage currentcancelation circuit receives at least one signal indicative of a commonmode current. The at least one signal indicative of the common modecurrent is received from: one or multiple input nodes of the powerconverter, one or multiple output nodes of the power converter, or theground node. The leakage cancelation current uses at least one signalindicative of the common mode current to generate the leakagecancelation current. After the leakage cancelation current is generated,the leakage cancelation current is supplied onto a node of the systemthereby causing net current on the power terminals to remainsubstantially near zero during operation of the power converter. Theleakage cancelation current may be supplied onto: one or multiple inputnodes of the power converter, one or multiple output nodes of the powerconverter, or the ground node.

In one example, a novel leakage current cancelation circuit is employedin an electric vehicle charging system. The leakage current cancelationcircuit is part of a charger module that includes a power converter, theleakage current cancelation circuit, a plurality of input terminals, aplurality of output terminals, and ground terminals. To charge theenergy storage system disposed within the electric vehicle, the electricvehicle is plugged into an electrical vehicle charging station toinitiate a charging operation. During the charging operation, thecharger module receives an Alternating Current (AC) supply onto the ACinput terminals, and the charger module generates and outputs positiveand negative Direct Current (DC) supply signals onto the outputterminals. The DC supply signals are supplied to circuitry internal tothe electric vehicle, such as the energy storage system.

During the charging operation, if a common mode current (or leakagecurrent) flows from circuitry within the electric vehicle onto theground node such that a GFI circuit of the charging station detectsimbalanced current on the charging conductors, then the GFI circuitdisables the charging station and the electric vehicle stops charging.Such flow of leakage current is undesirable because the electric vehiclewill not charge if the GFI circuit trips and disables charging. Theleakage current cancelation circuit generates and supplies a leakagecancelation current so that the leakage current is canceled and noimbalanced current on the charging conductors is detected by the GFIcircuit during normal charging conditions. Normal charging conditions isused to refer to a charging condition during which no short circuitexists within the internal circuitry of the electric vehicle, no shortcircuit exists between the high-voltage conductors and earth ground, andthe internal circuitry of the electric vehicle is operating as intendedby the manufacturer. Internal circuitry includes any electroniccomponent disposed within the electric vehicle, such as the powerconverter, motor inverters, system loads, or battery packs. If a shortcircuit condition exists, then the GFI circuit will trip and chargingoperation will be disabled to prevent damage to the electric vehiclecircuitry. The leakage current cancelation circuit will not prevent theGFI circuit from tripping during such a short circuit condition.

The leakage current cancelation circuit comprises a leakage cancelationcurrent generator and a charge injection circuit. In this example, theleakage cancelation current generator includes a microcontroller, acurrent reference generator circuit, and a current controlled feedbackcircuit. During charging operation, the current reference generatorcircuit receives a DC+ supply voltage signal output by the powerconverter onto a first input node and receives a DC− supply voltagesignal output by the power converter onto a second input node. The DC+and DC− supply voltage signals are signals indicative of the common modecurrent. The current reference generator circuit is controlled by themicrocontroller to generate a current reference voltage signal. Thecurrent controlled feedback circuit receives the current referencevoltage signal and generates the leakage cancelation current. The chargeinjection circuit supplies the generated leakage cancelation currentonto AC input nodes of the power converter. Current on the ground nodeis substantially near zero due to the injected leakage cancelationcurrent. In one example, current on the ground node is between −3.0milliamperes and +3.0 milliamperes during charging operation undernormal conditions.

In accordance with one novel aspect, the charger module is non-isolatedfrom the electric vehicle charging station and power source.Accordingly, the charger module, the electric vehicle charging station,the circuitry internal to the electric vehicle, and the power sourceshare a common ground. Isolated charger modules that include inductors,transformers, or similar type of magnetic devices are well known in theart. However, such isolated charger modules are expensive andprohibitively costly in some applications. In addition, isolated chargermodules tend to be large and difficult to install in some vehicles. Thenon-isolated charger module, on the other hand, includes no suchinductors, transformers, or magnetic devices. The power converter alsodoes not include any inductor, transformer, or magnetic device. Noinductor, transformer, or magnetic device is present in a powerconversion path of the power converter. No inductor, transformer, ormagnetic device is directly coupled to an output node of the powerconverter. This reduces the number of circuit components and complexityrequired to manufacture the power converter. As a result, thenon-isolated charger module is significantly cheaper to manufacture thantraditional isolated charger modules. Moreover, the non-isolated chargermodule is smaller than traditional isolated charger modules therebyyielding at least one-hundred and seventy watts of output per cubic inchof volume of the charger module.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequentlyit is appreciated that the summary is illustrative only. Still othermethods, and structures and details are set forth in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a high level diagram of an electric vehicle charging system10.

FIG. 2 is a more detailed diagram of electric vehicle charging system 10of FIG. 1.

FIG. 3 are waveform diagrams of the AC supply voltages and leakagecurrent 41 during charging of electric vehicle 13.

FIG. 4 is a perspective diagram of charging station 12 that includescable 21 and plug 19.

FIG. 5 is a diagram of an electrical power system 50 with a novelleakage current cancelation current 51.

FIG. 6 is a diagram of electric vehicle charging system 80 that employsa novel leakage current cancelation circuit 81.

FIG. 7 is a block diagram of leakage current cancelation circuit 81.

FIG. 8 is another block diagram of leakage current cancelation circuit81 that shows how leakage current cancelation circuit 81 prevents theGFI circuit within charging station 83 from tripping.

FIG. 9 is another block diagram of leakage current cancelation circuit81 that shows the current path 115 of the leakage cancelation current.

FIG. 10 is a detailed circuit diagram of electric vehicle chargingsystem 80 that includes the novel leakage current cancelation circuit81.

FIG. 11 is a diagram of a waveform 150 of leakage cancelation current149 that is to be injected onto AC input nodes 103.

FIG. 12 is a diagram of waveform 151 of the signal indicative of commonmode current 101.

FIG. 13 is a diagram of waveform 152 of common mode current 141 thatflows on ground conductor 85 during charging mode operation.

FIG. 14 is a diagram of output voltage of operational amplifier 137.

FIG. 15 is a detailed circuit diagram of another embodiment of a leakagecurrent cancelation circuit 160 that may also be employed to supply aleakage cancelation current onto AC input nodes 103.

FIG. 16 is a diagram of another embodiment of a leakage currentcancelation circuit 200 that may also be employed to supply a leakagecancelation current onto AC input nodes 103.

FIG. 17 is a diagram of another embodiment of a leakage currentcancelation circuit 220.

FIG. 18 is a diagram of a system 230 that employs another embodiment ofa charger module 231.

FIG. 19 is an equation 250 that shows the relationship between voltageson DC+ terminal 93 and DC− terminal 95, common mode capacitances C_POSand C_NEG, and the leakage cancelation current.

FIG. 20 is a more detailed diagram of the charger module 231.

FIG. 21 is a more detailed diagram of the microcontroller 260 andcurrent reference generator circuit 261.

FIG. 22 is a detailed circuit diagram of current reference generatorcircuit 261.

FIG. 23 shows an equation 321 for capacitance C_POS and an equation 322for capacitance C_NEG.

FIG. 24 is flowchart of a method 400 in accordance with one novelaspect.

FIG. 25 is a block diagram of current controlled feedback circuit 262.

FIG. 26 is a detailed circuit diagram of current controlled feedbackcircuit 262.

FIG. 27 is a diagram of waveforms at various nodes of charger module 231during charging mode operation.

FIG. 28 is a flowchart of a method 500 in accordance with another novelaspect.

FIG. 29 is a front view of charger module 231.

FIG. 30 is a side view of charger module 231.

FIG. 31 is a perspective view of charger module 231.

FIG. 32 is a flowchart of a method of manufacture 600.

FIG. 33 is a diagram of another embodiment of a leakage currentcancelation circuit 610.

FIG. 34 is a diagram of another embodiment of a current referencegenerator circuit 620.

FIG. 35 is a diagram of another embodiment of a current referencegenerator circuit 643.

FIG. 36 is a more detailed block diagram of current reference generatorcircuit 643.

FIG. 37 is a diagram of another embodiment of charge injection circuit670.

FIG. 38 is a diagram of an electric vehicle charging station 680 havinga novel leakage current cancelation circuit 681 and a conventional GFIcircuit 682.

FIG. 39 is a flowchart of a method 700 in accordance with another novelaspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a high level diagram of an electric vehicle charging system10. Electric vehicle charging system 10 includes an Alternating Current(AC) input source 11, an electric vehicle charging station 12, and anelectric vehicle 13. In this example, electric vehicle charging station12 is a CS-100 electric vehicle charging station available fromClipperCreek, Inc., located at 11850 Kemper Rd. #E, Auburn, Calif.95603. In another example, electric vehicle charging station 12 is anEvr-Green 400 Electric Vehicle Charging Station available from LevitonMfg. Company Inc., located at 201 North Service Rd., Melville, N.Y.11747. The electric vehicle 13 comprises a power converter 14, motorinverters 15, and a system load 16. Many additional components involvedin the structure and operation of electric vehicle 13 are excluded forexplanatory purposes.

Charging station 12 receives three-phase AC supply voltages from the ACinput source 11 and generates charge currents. The charge currents aresupplied onto a cable 21 comprising AC supply conductors 17 and a groundconductor 18. An end of the cable has a plug 19 that is insertable intoa socket 20 of electric vehicle 13. After plug 19 is inserted intosocket 20 of electric vehicle 13, battery packs (not shown) disposedwithin electric vehicle 13 are charged. For additional information onthe structure and operation of the electric vehicle charging station 12,see: (1) U.S. patent publication number 2014/0015487 entitled “ElectricVehicle Supply Equipment,” filed on Sep. 12, 2013; (2) U.S. patentpublication number 2012/0206100 entitled “Electric Vehicle SupplyEquipment,” filed on Apr. 25, 2012; (3) U.S. patent publication number2012/0091961 entitled “Electric Vehicle Supply Equipment With StorageConnector,” filed on Dec. 21, 2011; (4) U.S. patent publication number2011/0169447 entitled “Electric Vehicle Supply Equipment,” filed on Jan.11, 2010; and (5) U.S. Pat. No. 8,558,504 entitled “Electric VehicleSupply Equipment With Timer,” filed on Jun. 23, 2010 (the entire subjectmatter of each of these patent documents is incorporated herein byreference).

FIG. 2 is a more detailed diagram of electric vehicle charging system 10of FIG. 1. Electric vehicle charging system 10 includes a Ground FaultInterrupter (GFI) circuit 25 that detects current on ground conductor18. In this example, power converter 14 is a three-phase rectifiercircuit having diodes 26, 27, 28, 29, 30, and 31. Three-phase rectifiercircuit 14 is coupled to receive AC supply voltages from AC inputconductors 32 and generates a positive Direct Current (DC) voltagesignal 33 on DC+ conductor 34 and a negative DC voltage signal 35 on DC−conductor 36. DC+ conductor 34 is also referred to as a “positive supplyrail”, a “positive voltage rail”, a “DC+ rail”, a “positive supplyvoltage”, and a “positive rail”. Similarly, DC− conductor 36 is alsoreferred to as a “negative supply rail”, a “negative voltage rail”, a“DC− rail”, a “negative supply voltage”, and a “negative rail”. Positiveand negative DC voltage conductors 34 and 36 supply motor inverter 15and other circuitry represented by system load 16 of electric vehicle13.

Capacitances 37, 38, and 39 are parasitic or EMI filter capacitancesbetween power electronics conductors of electric vehicle 13 and vehiclechassis ground 40. A sum total of capacitances 37, 38, and 39 isreferred to as a common mode capacitance of system 10. Common modecapacitance is also referred to as a “leakage capacitance”. The term“leakage capacitance” is used interchangeably with the term “common modecapacitance” throughout the instant application. A common mode current(CMC) 41 flows from circuitry of electric vehicle 13 to vehicle chassisground 40 via capacitances 37, 38, and 39. Common mode current 41 isalso referred to as “leakage current”. The term “leakage current” isused interchangeably with the term “common mode current” throughout theinstant application. During charging of electric vehicle 13, plug 19 isconnected to socket 20 such that AC supply conductors 17 areelectrically coupled to AC input conductors 32 and ground conductor 18is electrically coupled to vehicle chassis ground 40. Leakage current 41flows from circuitry of electric vehicle 13 (for example, three-phaserectifier 14, motor inverter 15, and system load 16) to vehicle chassisground 40 via capacitances 37, 38, and 39, through socket 20, throughplug 19, and onto ground conductor 18.

GFI circuit 25 of electric vehicle charging station 12 is coupled todetect a current level of leakage current 41 flowing on ground conductor18. If GFI circuit 25 determines that a current level of leakage current41 exceeds a pre-determined threshold current level, then the GFIcircuit 25 disables charging station 12 thereby stopping charging ofbattery packs within electric vehicle 13. GFI circuit 25 operates inthis fashion to protect the circuitry within electric vehicle 13. Forexample, if a electrical short is present within circuitry of electricvehicle 13, then during charging, the current level of the leakagecurrent 41 on ground node 18 may spike exceeding the pre-determinedthreshold current level and preventing further damage to the circuitrywithin electric vehicle 13. Unfortunately, even when the circuitrywithin electric vehicle 13 is operating as desired, the leakage current41 may exceed the pre-determined threshold current level causingelectric vehicle charging station 12 to cease charging.

FIG. 3 are waveform diagrams of the AC supply voltages and leakagecurrent 41 during charging of electric vehicle 13. Waveforms 23 are theAC supply voltages on AC supply conductors 17 and AC input conductors 32when electric vehicle 13 is plugged into charging station 12 duringcharging. The AC supply voltages are supplied from AC input source 11,through electric vehicle charging station 12, and onto three-phaserectifier 14 of electric vehicle 13 via cable 21, plug 19, and socket20. Waveform 24 is leakage current 41 on vehicle chassis groundconductor 40 and ground conductor 18 during charging. In this example,GFI circuit 25 of charging station 12 is configured to interruptcharging when the current level of leakage current 41 exceeds twentymilliamps. Charging operation begins at time T0. At time T1, leakagecurrent 41 exceeds the twenty milliamp threshold current and GFI circuit25 of charging station 12 trips causing charging to be disabled.Waveforms 23 and 24 are dashed after time T1 showing that the electricvehicle is no longer charging.

FIG. 4 is a perspective diagram of charging station 12 that includescable 21 and plug 19. Cable 21 forms a protective enclosure around ACsupply conductors 17, ground conductor 18, and additional signalconductors (not shown). To initiate charging, plug 19 is inserted intosocket 20 of electric vehicle 13. As explained above, if GFI circuit 25detects that the current level of leakage current 41 on ground conductor18 exceeds the pre-determined threshold current level, then GFI circuit25 disables charging station 12 and charging ceases.

FIG. 5 is a diagram of an electrical power system 50 with a novelleakage current cancelation current 51. Although common mode current maypresent challenges in charging an electric vehicle, a skilled artisanappreciates that common mode current may be undesirable in many otherapplications involving power converters. Electrical power system 50comprises leakage current cancelation circuit 51, a power converter 52,and a load 53. Power converter 52 is coupled to power supply 54 viaconductors 55 and 56. Power converter 52 receives supply current signals57 and 58 from power supply 54 and generates and outputs supply signals59 and 60. Supply signals 59 and 60 drive load 53 via conductors 61 and62. A first parasitic capacitance 63 is coupled between conductor 61 anda ground node 64. A second parasitic capacitance 65 is coupled betweenconductor 62 and the ground node 64. Summing first parasitic capacitance63 and second parasitic capacitance 65 yields a common mode capacitance66 of system 50. Reference numeral 67 identifies input nodes of powerconverter 52, and reference numeral 68 identifies output nodes of powerconverter 52.

Leakage current cancelation circuit 51 includes a leakage cancelationcurrent generator 69, at least one input node 70, and at least oneoutput node 71. Leakage current cancelation circuit 51 receives at leastone signal indicative of common mode current 72 onto at least one inputnode 70. The at least one signal indicative of common mode current 72 isreceived from input nodes 67 of power converter 52, from output nodes 68of power converter 52, or from ground node 64. Typically, two signalsindicative of common mode current are received, a first onto a firstinput node and a second onto a second input node. Leakage cancelationcurrent generator 69 uses the received at least one signal indicative ofcommon mode current 72 to generate at least one leakage cancelationcurrent 73 onto at least one output node 71. The at least one leakagecancelation current 73 is supplied to input nodes 67 of power converter52, to output nodes 68 of power converter 52, or to ground node 64.Depending on where the leakage cancelation currents, multiple leakagecancelation currents may be generated and supplied onto varying numbersof conductors.

During operation of power converter 52, power converter supply currentsignals 57 and 58 flow between power converter 52 and power supply 54.Ideally, supply current signal 57 flowing into power converter 52 wouldhave a magnitude equal to a magnitude of supply current signal 58flowing out of power converter 52. However, due to common modecapacitance 66 of system 50, common mode current or leakage current 75flows from conductors 61 and 62 to ground node 64 via capacitances 63and 65. As a result, magnitudes of supply current signal 57 and supplycurrent signal 58 are not equivalent. In typical applications, leakagecurrent 75 is undesirable and is to be minimized.

Leakage current cancelation circuit 51 operates to cancel leakagecurrent 75 by generating and supplying leakage cancelation current 73onto at least one node of electrical system 50. Leakage cancelationcurrent 73 has a magnitude opposite that of leakage current 75 such thatan instantaneous sum of leakage current 75 and leakage cancelationcurrent 73 is substantially zero. In one example, the instantaneous sumof leakage current 75 and leakage cancelation current 73 during chargingoperation is within a range having a lower bound of −5.0 milliamperesand an upper bound of +5.0 milliamperes. In another example, theinstantaneous sum of leakage current 75 and leakage cancelation current73 during charging operation is within a range having a lower bound of−3.0 milliamperes and an upper bound of +3.0 milliamperes. Leakagecancelation current 73 may also be referred to as a “leakage nullingcurrent”. Various embodiments of leakage current cancelation circuit 51and how each embodiment operates in the electrical power system are setforth below.

FIG. 6 is a diagram of electric vehicle charging system 80 that employsa novel leakage current cancelation circuit 81. Electric vehiclecharging system 80 includes an AC input source 82, an electric vehiclecharging station 83, an electric vehicle 84, and a ground conductor 85.Electric vehicle 84 comprises a novel charger module 86, motor inverters87, and a system load 88. When electric vehicle 84 is coupled toelectric vehicle charging station 83 in a charging mode, charger module86 receives a three phase AC supply from electric vehicle chargingstation 83 onto terminals 89, 90, and 91 via AC input conductors 92.Charger module 86 outputs a positive DC supply voltage onto DC+conductor 93 via terminal 94, and a negative DC supply voltage onto DC−conductor 95 via terminal 96. Ground conductor 85 is coupled to vehiclechassis ground 97 via ground terminals 98 and 99.

Charger module 86 includes a power converter 100 and the leakage currentcancelation circuit 81. In this example, power converter 100 is anAC-to-DC three phase rectifier circuit that receives an AC supply andoutputs a DC supply used to power internal circuitry of electric vehicle84. Leakage current cancelation circuit 81 receives a signal indicativeof common mode current 101 from vehicle chassis ground 97 via groundterminal 99. In this example, the signal indicative of common modecurrent 101 is the leakage current present on vehicle chassis ground 97.Leakage current cancelation circuit 81 generates leakage cancelationcurrents 102 from the received signal indicative of common mode current101 and supplies leakage cancelation currents 102 onto AC input nodes103. As a result of supplying leakage cancelation currents 102 onto ACinput nodes 103, current levels on ground conductor 85 remain below apre-determined current level preventing charging station 83 fromdisabling the charging operation.

FIG. 7 is a block diagram of leakage current cancelation circuit 81.Leakage current cancelation circuit 81 includes current sense circuitry110, amplifier circuitry 111, and charge injection circuitry 112.Current sense circuitry 110 and amplifier circuitry 111 form the leakagecancelation current generator. Current sense circuitry 110 senses signalindicative of common mode current 101 on vehicle chassis ground 97 andgenerates a sensed leakage current signal 112 that is supplied toamplifier circuitry 111. Amplifier circuitry 111 generates and suppliesleakage cancelation current 113 to charge injection circuitry 112.Charge injection circuitry 112 injects leakage cancelation current 113onto AC input nodes 103. During charging mode, a current level ofleakage current 114 on ground conductor 85 is maintained below thepredetermined current level of the GFI circuit within charging station83.

FIG. 8 is another block diagram of leakage current cancelation circuit81 that shows how leakage current cancelation circuit 81 prevents theGFI circuit within charging station 83 from tripping. Amplifiercircuitry 111 is realized as a high gain amplifier. High gain amplifier111 maintains the current level of leakage current 114 on groundconductor 85 substantially near a zero current level.

FIG. 9 is another block diagram of leakage current cancelation circuit81 that shows the current path 115 of the leakage cancelation current.The leakage current path 115 extends from vehicle chassis groundconductor 97, through amplifier circuitry 111, through charge injectioncircuitry 112, and onto AC input nodes 103.

FIG. 10 is a detailed circuit diagram of electric vehicle chargingsystem 80 that includes the novel leakage current cancelation circuit81. Electric vehicle charging station 83 includes GFI circuit 120.Typically, a manufacturer of the charging station 83 sets apre-determined current at which GFI circuit 120 is tripped in compliancewith a standard, such as UL 2231. Rectifier 100 includes diodes 121,122, 123, 124, 125, and 126. Motor inverter 87 includes a capacitor 127that provides a model of electrical characteristics of the motorinverters. System load 88 includes a resistor 128 that provides a modelof electrical characteristics of the load. Parasitic capacitance 129represents the common mode capacitance of system 80. Leakage currentcancelation circuit 81 includes transformer 130, current sense circuitry131, amplifier circuitry 132, and charge injection circuitry 133.Transformer 130, current sense circuitry 131, and amplifier circuitry132 form the leakage cancelation current generator. Amplifier circuitry132 includes a voltage source 134, resistive divider network 135 and136, amplifier 137, capacitors 138 and 139, and resistors 140 and 141.Charge injection circuitry 133 includes resistor 142 and capacitors 143,144, and 145. The transformer has a first winding 153 and a secondwinding 147.

When electric vehicle 84 is coupled to charging station 83 in a chargingmode, current sense circuitry 131 senses a signal 146 proportional tothe signal indicative of common mode current 101 through second winding147 of transformer 130. Current sense circuitry 131 outputs signal 148onto amplifier circuitry 132. Amplifier circuitry 132 generates aleakage cancelation current 149 from received signal 148, and amplifiercircuitry 132 injects leakage cancelation current 102 onto AC inputnodes 103 via charge injection circuitry 133.

FIGS. 11-14 are waveform diagrams along various nodes of system 80during charging mode of operation. FIG. 11 is a diagram of a waveform150 of leakage cancelation current 149 that is to be injected onto ACinput nodes 103. FIG. 12 is a diagram of waveform 151 of the signalindicative of common mode current 101. Waveform 150 is of oppositemagnitude of waveform 151 such that an instantaneous sum of bothwaveforms is approximately zero. FIG. 13 is a diagram of waveform 152 ofcommon mode current 141 that flows on ground conductor 85 duringcharging mode operation. As shown in FIG. 13, the current level ofwaveform 152 does not exceed the twenty milliamp GFI pre-determinedcurrent level. Because the threshold current is never exceeded, GFIcircuit 120 will not disable charging station 83 during when theelectric vehicle 84 is charging. FIG. 14 is a waveform diagram of anoutput voltage of the operational amplifier 137 of FIG. 10.

FIG. 15 is a detailed circuit diagram of another embodiment of a leakagecurrent cancelation circuit 160 that may also be employed to supply aleakage cancelation current onto AC input nodes 103. Leakage currentcancelation circuit 160 includes current sense circuitry 161, amplifiercircuitry 162, and charge injection circuitry 163. Current sensecircuitry 161 and amplifier circuitry 162 form the leakage cancelationcurrent generator. Current sense circuitry 161 includes a transformer164 and resistor 165. Amplifier circuitry 162 comprises a voltage source166, resistive divider network 167 and 168, capacitors 169, 170, 171,172, 173, and 174, resistors, 177, 178, 179, 180, 181, 182, and 183, andamplifiers 184 and 185. In this example, amplifier 184 is a LT1126 DualDecompensated Low Noise, High Speed Precision Operational Amplifier,available from Linear Technology located at 720 Sycamore Dr., Milpitas,Calif. 95035. Amplifier 185 is an OPA547 High-Voltage, High-CurrentOperational Amplifier available from Texas Instruments Incorporatedlocated at 12500 TI Boulevard, Dallas, Tex. 75243. Charge injectioncircuit 163 includes resistor 186 and capacitors 187, 188, and 189. Thesignal indicative of common mode current 101 is sensed by current sensecircuit 161. Amplifier circuitry 162 receives sensed signal 190 andgenerates leakage cancelation current 191 that is injected into AC inputnodes 103 via charge injection circuit 163.

FIG. 16 is a diagram of another embodiment of a leakage currentcancelation circuit 200 that may also be employed to supply a leakagecancelation current onto AC input nodes 103. Leakage current cancelationcircuit 200 comprises current sense circuitry 201, amplifier 202,modulator integrated circuit 203, a driver integrated circuit 204,transistors 205 and 206, and a charge injection circuit 207. Currentsense circuitry 201, amplifier 202, modulator integrated circuit 203, adriver integrated circuit 204, and transistors 205 and 206 form theleakage cancelation current generator. Charge injection circuit 207includes a resistor 208, an inductor 209, and a capacitor 210. Duringcharging mode operation, current sense circuitry 201 receives the signalindicative of common mode current 101 on vehicle chassis ground 97 andoutputs sense signal 211. Amplifier 202 receives sense signal 211 andsupplies an amplified sense signal 212 onto modulator integrated circuit203. Modulator integrated circuit 203 supplies Pulse Width Modulated(PWM) signal 213 onto driver integrated circuit 204. Driver 204 controlstransistors 205 and 206 to switch such that the current level of leakagecurrent 114 is maintained substantially near zero. In one example,transistors 205 and 206 are realized as metal oxide semiconductorfield-effect transistors (MOSFETs). In another example, transistors 205and 206 are realized as insulated-gate bipolar transistors (IGBTs).

FIG. 17 is a diagram of another embodiment of a leakage currentcancelation circuit 220. Leakage current cancelation circuit 220comprises current sense circuitry 221, amplifier circuitry 222, andcharge injection circuitry 223. Current sense circuitry 221 andamplifier circuitry 222 form the leakage cancelation current generator.Leakage current cancelation circuit 220 operates in substantially thesame fashion as leakage current cancelation circuit 81 of FIG. 6, exceptthat leakage current cancelation circuit 220 is employed in a systemthat involves a DC-to-DC power converter instead of AC-to-DC powerconverter 100. In the example of FIG. 17, charge injection circuitry 223supplies leakage cancelation current 224 onto DC+ and DC− input nodes ofthe DC-to-DC power converter.

FIG. 18 is a diagram of a system 230 that employs another embodiment ofa charger module 231. Charger module 231 includes a power converter 232and a leakage current cancelation circuit 233. In the example of FIG.18, leakage capacitance 236 (or common mode capacitance) involves afirst parasitic capacitance 234 and a second parasitic capacitance 235.First parasitic capacitance 234 has a capacitance of C_POS and a voltagedrop of V_POS, and second parasitic capacitance 235 has a capacitance ofC_NEG and a voltage drop of V_NEG. Leakage capacitance 236 of system 230is equivalent to a sum of capacitances C_POS and C_NEG. Leakage current237 (or common mode current) flows from positive DC+ conductor 93 andfrom negative DC− conductor 95 onto vehicle chassis ground 97. In theexample of FIG. 18, vehicle chassis ground 97 is directly coupled toground node 85 without any intervening circuitry or discrete circuitdevices. Charger module 231 does not include any transformers,inductors, or any type of magnetic devices.

In accordance with one novel aspect, leakage current cancelation circuit233 receives a first signal indicative of a common mode current 238 anda second signal indicative of a common mode current 239. First signalindicative of a common mode current 238 is labeled as “DC+ signal” inFIG. 18 and second signal indicative of a common mode current 239 islabeled as “DC− signal” in FIG. 18. Leakage current cancelation circuit233 a generates leakage cancelation current from the received DC+ signal238 and DC− signal 239. Leakage current cancelation circuit 233generates leakage cancelation current without directly sensing thecommon mode current 237 on vehicle chassis ground 97 or ground node 85.Leakage current cancelation circuit injects the leakage cancelationcurrents ILCC_1, ILCC_2, and ILCC_3 onto AC input nodes 240 of the powerconverter 232. Reference numeral 241 identifies the injected leakagecancelation currents.

Charger module 231 is a seven terminal device. Terminals 242, 243, and244 are AC input terminals that receive AC power from charging station83. Terminal 245 is a ground terminal that couples vehicle chassisground 97 to ground node 85. Terminal 246 is another ground terminalthat is coupled to vehicle chassis ground 97. Charger module 231 isreferred to as “non-isolated” because vehicle chassis ground 97 iscoupled to ground node 85 and vehicle chassis ground 97 is not coupledto a separate ground node. Terminal 247 is a DC+ terminal that iscoupled to supply a DC+ supply voltage onto DC+ conductor 93. Terminal248 is a DC− terminal that is coupled to supply a DC− supply voltageonto DC− conductor 95.

FIG. 19 is an equation 250 that shows the relationship between voltageson DC+ terminal 93 and DC− terminal 95, parasitic capacitances C_POS andC_NEG, and the leakage cancelation current. Leakage current cancelationcircuit 233 generates the leakage cancelation current in accordance withequation 250. Equation 250 shows that if parasitic capacitances C_POSand C_NEG for electric vehicle 84 are known, then the desired leakagecancelation current may be generated by sensing the voltages on DC+terminal 93 and DC− terminal 95 during a charging operation and withoutdirectly sensing leakage current 237 (or common mode current).

FIG. 20 is a more detailed diagram of the charger module 231. In thisexample, power converter 232 is a three-phase rectifier circuit havingdiodes 251, 252, 253, 254, 255, and 256. Three-phase rectifier circuit232 is coupled to receive AC supply voltages from AC input conductors240 and to generate a positive Direct Current (DC) voltage signal 257 onDC+ conductor 93 and a negative DC voltage signal 258 on DC− conductor95. Positive and negative DC voltage conductors 93 and 95 supply motorinverter 87 modeled by capacitor 127 and system load 88 modeled byresistor 128.

Leakage current cancelation circuit 233 comprises a microcontroller 260,a current reference generator circuit 261, a current controlled feedbackcircuit 262, and a charge injection circuit 263. Microcontroller 260,current reference generator circuit 261, and current controlled feedbackcircuit 262 form the leakage cancelation current generator.Microcontroller supplies a multi-bit digital control signal 264 tocurrent reference generator circuit 261 via conductors 265. Multi-bitdigital control signal 264 sets a first configurable gain and a secondconfigurable gain of the current reference generator circuit 261 asexplained in connection with FIGS. 23 and 24. Current referencegenerator circuit 261 also receives a DC+ voltage signal 238 viaconductor 266 and DC− voltage signal 239 via conductor 267. Currentreference generator circuit 261 generates a current reference voltagesignal 268 from the received DC+ voltage signal 238, DC− voltage signal239, and multi-bit digital control signal 264. Current reference voltagesignal 268 is supplied onto current controlled feedback circuit 262 viaconductor 269. Current controlled feedback circuit 262 generates leakagecancelation current 270 from the received current reference voltagesignal 268. Leakage cancelation current 270 is injected onto AC inputnodes 240 via conductor 271 and charge injection circuit 263. Chargeinjection circuit 263 includes a resistor 272 and capacitors 273, 274,and 275. Charge injection circuit 263 supplies the leakage cancelationcurrent onto AC input nodes 240 as three separate currents, ILCC_1,ILCC_2, and ILCC_3.

In accordance with one novel aspect, power converter 232 of chargermodule 231 does not include any inductors, transformers, or magneticdevices. No inductor, transformer, or magnetic device is present in apower conversion path of power converter 232. For example, no inductoror transformer is coupled between an output node of power converter 232and DC+ terminal 247 or DC− terminal 248. DC+ signal 257 and DC− signal258 are supplied directly onto internal circuitry of electric vehicle 84without any intervening inductor or transformer. No inductor,transformer, or magnetic device is coupled to an output node of powerconverter 232. Power converter 232 has six and only six diodes 251-256,and no additional circuitry is disposed between an input node and anoutput node of power converter 232.

FIG. 21 is a more detailed diagram of the microcontroller 260 andcurrent reference generator circuit 261. Current reference generatorcircuit 261 includes a first voltage divider 280, a second voltagedivider 281, a first configurable gain circuit 282, a secondconfigurable gain circuit 283, summing amplifier circuit 284,differentiator circuit 285, and a voltage gain circuit 286.Microcontroller 260 includes interface circuitry 287, a processor 288,and memory 289. An amount of processor executable instructions 290 isstored in memory 289. Processor 288 reads the amount of processorexecutable instructions 290 via communication bus 291. Executinginstructions 290 cause multi-bit digital control signal 264 to besupplied to current reference generator circuit 261 via conductors 265.A first portion of the multi-bit digital control signal 264 sets firstconfigurable gain circuit 282 to a gain G_POS via conductors 292. Asecond portion of the multi-bit digital control signal 264 sets secondconfigurable gain circuit 283 to a gain G_NEG via conductors 293. Firstconfigurable gain circuit 282 receives signal 294 from first voltagedivider 280, voltage amplifies signal 294 by G_POS, and suppliesamplified signal 295 onto a first input of summing amplifier circuit284. Second configurable gain circuit 283 receives signal 296 fromsecond voltage divider 281, voltage amplifies signal 296 by G_NEG, andsupplies an amplified signal 297 onto a second input of summingamplifier circuit 284. Summing amplifier circuit 284 sums signals 295and 297 and voltage amplifies the resulting sum by G_SUM. Summingamplifier circuit 284 supplies amplified signal 298 onto differentiatorcircuit 285 which in turn outputs signal 299 onto voltage gain circuit286. Voltage gain circuit 286 voltage amplifies the received signal 299by G_DIFF and generates current reference voltage signal 268. Voltagegain circuit 286 supplies current reference voltage signal 268 ontocurrent controlled feedback circuit 262 via conductor 269.

FIG. 22 is a detailed circuit diagram of current reference generatorcircuit 261. First voltage divider 280 comprises resistors 300 and 301.Second voltage divider 281 comprises resistors 302 and 303. Firstconfigurable gain circuit 282 comprises a voltage gain amplifier 304.Second configurable gain circuit 283 comprises a voltage gain amplifier305. Summing amplifier circuit 284 comprises input resistors 306 and307, operational amplifier 308, capacitors 309, 310, and 311, andresistor 312.

Differentiator circuit 285 includes an RC filter comprising capacitor313 and resistor 314. Voltage gain circuit 286 comprises input resistor315, differential amplifier 316, capacitors 317, 318, and 319, andresistor 320.

FIG. 23 shows an equation 321 for capacitance C_POS and an equation 322for capacitance C_NEG. As shown in equations 321 and 322, the gain G_POSand gain G_NEG are configured by microcontroller 260 as shown in FIG.21. If the parasitic capacitances C_POS and C_NEG are known for anelectric vehicle, then microcontroller 260 can configure gain G_POS andgain G_NEG accordingly so that the desired leakage current can begenerated according to equation 250 shown in FIG. 19.

FIG. 24 is flowchart of a method 400 in accordance with one novelaspect. In a first step (step 401), a common mode capacitance (orleakage capacitance) of an electric vehicle is determined. For example,in FIG. 18, common mode capacitance 236 of electric vehicle 84 isdetermined by obtaining capacitances for each electronic component ofelectric vehicle 85 from specifications provided by the manufacturer ofthe electronic component. Typically, such specifications refer to thecapacitances as a “Y-capacitor”, an “EMI capacitor”, an “internal commonmode capacitor”, or “a common mode capacitor”. The common modecapacitance is then determined from all of the obtained parasiticcapacitances.

In a second step (step 402), a first voltage gain of a firstconfigurable gain circuit and a second voltage gain of a secondconfigurable gain circuit are configured according to the common modecapacitances determined in step 401. A first digital control signal setsthe first voltage gain and a second digital control signal sets thesecond voltage gain. For example, in FIG. 22, first digital signal 403sets voltage gain G_POS of configurable gain circuit 304 and seconddigital signal 404 sets voltage gain G_NEG of configurable gain circuit305.

FIG. 25 is a block diagram of current controlled feedback circuit 262.Current controlled feedback circuit 262 comprises output current sensecircuit 410, reference current error amplifier 411, and a resistor 412.Output current sense circuit 410 and reference current error amplifier411 form a control loop 413 that ensures leakage cancelation current 270to be injected is controlled as desired. Reference current erroramplifier 411 receives current reference voltage signal 268 from currentreference gain circuit 261 via conductor 269 and also receives outputcurrent sense voltage signal 414 from output current sense circuit 410via conductor 415. Output current sense circuit 410 generates outputcurrent sense voltage signal 414 by sensing current through resistor412.

FIG. 26 is a detailed circuit diagram of current controlled feedbackcircuit 262. Output current sense circuit 410 includes resistors 420,421, 422, and 423, capacitors 424 and 425, and operational amplifier426. Reference current error amplifier 411 includes resistors 427, 428,and 429, capacitors 430, 431, 432, 433, 434, and 435, zener diodes 436and 437, and amplifier 438.

FIG. 27 is a diagram of waveforms at various nodes of charger module 231during charging mode operation. Waveform 440 is the output voltage ofoperational amplifier 438. Waveform 441 is current reference voltagesignal 268 generated by current reference generator circuit 261 andsupplied onto conductor 269. Waveform 442 is a single phase of the ACsupply voltage supplied by charging station 83 on one of the AC inputnodes 240. Waveform 443 is leakage current 237 (or common mode current)present on ground node 85. As shown in FIG. 27, leakage current 237 doesnot exceed pre-determined current level of GFI circuit 120 and chargingoperation will not be affected by leakage current 237 under normaloperating conditions.

FIG. 28 is a flowchart of a method 500 in accordance with another novelaspect. In a first step (step 501), a first voltage signal is receivedonto a first input node of a leakage current cancelation circuit and asecond voltage signal is received onto a second input node of theleakage current cancelation circuit. The first and second voltagesignals are signals indicative of common mode current of an electricvehicle. For example, in FIG. 20, current reference generator circuit261 of leakage current cancelation circuit 233 receives DC+ voltagesignal 238 and DC− voltage signal 239. DC+ voltage signal 238 and DC−voltage signal 239 are signals indicative of common mode current 237 ofelectric vehicle 84.

In a second step (step 502), a leakage cancelation current is generatedusing the received first and second signals indicative of the commonmode current. No inductor, transformer, or magnetic device is involvedin generating the leakage cancelation current. In the example of FIG.20, microcontroller 260, current reference generator circuit 261, andcurrent controlled feedback circuit 262 operate to generate a leakagecancelation current 270. Current reference generator circuit 261receives DC+ voltage signal 238 and DC− voltage signal 239 and generatesa current reference voltage signal 268 by performing analog amplifying,summing, and differentiation functions in accordance with equation 250of FIG. 19. Current controlled feedback circuit 262 receives currentreference voltage signal 268 and generates and outputs leakagecancelation current 270. No inductor, transformer, or magnetic device isinvolved in generating leakage cancelation current 270.

In a third step (step 503), a leakage cancelation current is suppliedonto at least one node of the electrical power system such that duringoperation of the power converter a current level on the ground node issubstantially zero. No inductor or transformer is involved in supplyingthe leakage cancelation current. For example, in FIG. 20, currentcontrolled feedback circuit 262 generates leakage cancelation current270 and is injected onto AC input nodes 240 via charge injection circuit263. As shown in waveform 443, the current level at ground node 85 doesnot exceed +/−3.0 mA. In addition, the pre-determined current level ofGFI circuit 120 is not exceeded and charging operation will not beinterrupted under normal conditions.

FIGS. 29, 30, and 31 illustrate various views of charger module 231.FIG. 29 is a front view of charger module 231. FIG. 30 is a side view ofcharger module 231. FIG. 31 is a perspective view of charger module 231.Charger module 231 includes a metal enclosure 510, output terminals 511and 512, and input terminals 513, 514, and 515. Output terminals 511 and512 provide the DC supply to circuitry within electric vehicle 84. Inputterminals 513, 514, and 515 receive the AC supply from charging station83. Centers of adjacent input terminals 513, 514, and 515 are spaced adistance D1 from each other. Centers of adjacent output terminals 511and 512 are spaced a distance D2 from each other. Distance D1 issubstantially equivalent to distance D2. As a result of not includingany magnetic components, such as transformers, inductors, and HallEffect devices, charger module 231 is more compact than conventionalcharger modules. Due to the compact structure, charger module 231outputs at least one-hundred and seventy watts of output per cubic inchof volume of the charger module. The height of charger module 231 isless than six times distance D1. The length of charger module 231 isless than seven times distance D1. The width of charger module 231 isless than distance D1.

FIG. 32 is a flowchart of a method of manufacture 600. In a first step(step 601), a power converter and a leakage current cancelation circuitare enclosed in metal enclosure to form a charger module. The powerconverter is coupled to receive a leakage cancelation current generatedby the leakage current cancelation circuit. The leakage currentcancelation circuit cancels the common mode current exhibited by thepower converter when the charger module is employed in an electricalsystem. For example, in FIG. 31, a metal enclosure 510 surrounds powerconverter 232 and leakage current cancelation circuit 233 forming acharger module 231.

FIG. 33 is a diagram of another embodiment of a leakage currentcancelation circuit 610. Leakage current cancelation circuit 610 issubstantially similar to leakage cancelation circuit 233 of FIG. 20,except that leakage current cancelation circuit 610 includes a switchrelay 611. Microcontroller 612 supplies digital control signal 613 ontoswitch relay 611 via conductor 614. Digital control signal 613 controlsswitch relay 611 to switch on and to switch off. Initially when chargingoperation is activated, transients from the AC supply lines may beundesirably injected onto the charger module. To prevent suchundesirable effects, microcontroller 612 controls switch relay 611 toswitch off for a startup delay time period when charging operation isinitiated. After the startup delay time period, microcontroller 612controls switch relay 611 to switch on. The startup delay time period istypically between two-hundred milliseconds and five-hundredmilliseconds. Leakage current cancelation circuit 610 is not activateduntil after the startup delay time period and no leakage cancelationcurrent 270 is generated.

FIG. 34 is a diagram of another embodiment of a current referencegenerator circuit 620. Current reference generator circuit 620 operatessimilarly to current reference generator circuit 261 of FIG. 22, exceptthat the current reference generator circuit 620 generates currentreference voltage signal 621 with digital logic rather than analogcircuitry. Current reference generator circuit 620 includes the firstvoltage divider 280, the second voltage divider 281, and amicrocontroller 622. Microcontroller 622 comprises a firstAnalog-to-Digital Converter (ADC) 623, second ADC 624, a processor 625,memory 626, a Digital-to-Analog Converter (DAC) 627, and a communicationbus 628. Memory 626 stores an amount of processor executableinstructions 629. Processor executable instructions 629 comprise asumming module 630 and a differentiator module 631. By executingProcessor executable instructions 629, microcontroller 622 performs inthe digital domain the same functions performed by analog circuitry 284,285, and 286 of FIG. 22. Processor executable instructions 629 forsumming and differentiating, such as in analog circuitry 284, 285, and286 of FIG. 22, are known in the art.

FIG. 35 is a diagram of another embodiment of a current referencegenerator circuit 643. Current reference generator circuit 643 andcurrent controlled feedback circuit 262 form the leakage cancelationcurrent generator. Current reference generator circuit 643 receives theDC+ supply current signal 644 from current sense circuit 645. In oneexample, current sense circuit 645 is realized as a transformer or aHall-effect current sensor device. In this example, current referencegenerator circuit 643 receives only one signal indicative of the leakagecurrent of electric vehicle 84 which is DC+ supply current signal 644.Current reference generator circuit 643 comprises a current sensecircuit 648, amplifier circuits 649, 650, and 651, and a microcontroller652. Current reference generator circuit 643 employs digital techniquesto generate current reference voltage signal 653 that is supplied ontocurrent controlled feedback circuit 262.

FIG. 36 is a more detailed block diagram of current reference generatorcircuit 643. Microcontroller 652 comprises ADCs 654, 655, 656, and 657,a processor 658, memory 659, a PWM circuit 660, and communication bus661. Memory 659 stores an amount of processor executable instructions662 that includes a voltage ripple model instruction 663. By sensingcurrent on the DC+ conductor 93, the voltage ripple model is used togenerate current reference voltage signal 653.

FIG. 37 is a diagram of another embodiment of charge injection circuit670. Charge injection circuit 670 comprises a transformer 671 having afirst winding 672 and a second winding 673. First winding 672 is coupledbetween conductor 271 and another ground node 674. Ground node 674 isisolated from ground node 85. Second winding 673 is coupled betweencapacitors 273, 274, and 275 and vehicle chassis ground 97.

FIG. 38 is a diagram of an electric vehicle charging station 680 havinga novel leakage current cancelation circuit 681 and a conventional GFIcircuit 682. Leakage current cancelation circuit 681 receives a signalindicative of common mode current 683 from digital logic circuitry 684within the electric vehicle via common mode current terminal 685.Microcontroller 260, current reference generator circuit 261, andcurrent controlled feedback circuit 262 form the leakage cancelationcurrent generator disposed within the charging station 680. Leakagecurrent cancelation circuit 681 generates a leakage cancelation current686 in a substantially similar fashion as leakage current cancelationcircuit 233 of FIG. 20. Leakage current cancelation circuit 681 suppliesthe leakage cancelation current 686 onto AC supply nodes 687 via chargeinjection circuit 263.

FIG. 39 is a flowchart of a method 700 in accordance with another novelaspect. In a first step (step 701), an electric vehicle charging stationis provided that includes a GFI circuit and a leakage currentcancelation circuit. The electric vehicle charging station includes acommon mode current terminal coupled to receive a signal indicative of acommon mode current (or leakage current) from circuitry within anelectric vehicle. During charging of the electric vehicle, the leakagecurrent cancelation circuit generates a leakage cancelation current fromthe signal indicative of the common mode current. In the example of FIG.38, electric vehicle charging station 680 is provided and includes GFIcircuit 682 and leakage current cancelation circuit 681. Common modecurrent terminal 685 receives signal 683 indicative of common modecurrent and generates leakage cancelation current 686 that is injectedonto AC supply nodes 687.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. For example, although leakage current cancelationcircuit 233 of FIG. 18 involved three phase charging, the leakagecurrent cancelation circuit 233 may also be employed in a split-phasecharging system. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A leakage current cancelation circuit that ispart of an electrical power system having a power converter, a load, anda ground node, the leakage current cancelation circuit comprising: afirst input node that receives a first signal from a first node, whereina common mode current is present on the ground node during operation ofthe electrical power system, and wherein the first node is selected fromthe group consisting of: an input node of the power converter, an outputnode of the power converter, and a node coupled to the ground node; aleakage cancelation current generator that receives the first signalfrom the first input node, wherein the leakage cancelation currentgenerator generates a leakage cancelation current without directlysensing the common mode current; and a first output node, wherein theleakage cancelation current that is generated by the leakage cancelationcurrent generator is supplied onto the first output node, and whereinthe output node is coupled to a second node selected from the groupconsisting of: an input node of the power converter, an output node ofthe power converter, and a node coupled to the ground node.
 2. Theleakage current cancelation circuit of claim 1, wherein the powerconverter is supplied by an electrical power source, wherein the powerconverter, leakage current cancelation circuit, and the electrical powersource share common ground, and wherein the electrical power system hasone and only one ground node.
 3. The leakage current cancelation circuitof claim 1, wherein the power converter and the leakage currentcancelation circuit are parts of a charger module that supplies theload.
 4. The leakage current cancelation circuit of claim 1, wherein noinductor, transformer, or magnetic device is involved in generating theleakage cancelation current.
 5. The leakage current cancelation circuitof claim 1, wherein the leakage cancelation current has a magnitudesubstantially equal to a magnitude of the common mode current undernormal charging conditions, and wherein the leakage cancelation currenthas a sign opposite a sign of the common mode current under normalcharging conditions.
 6. The leakage current cancelation circuit of claim1, wherein the power converter is selected from the group consisting ofan AC-to-AC power converter, an AC-to-DC power converter, a DC-to-DCpower converter, and a DC-to-AC power converter.
 7. The leakage currentcancelation circuit of claim 1, wherein the first input node is coupledto a first output node of the power converter, and wherein the leakagecurrent cancelation circuit further comprises: a second input node thatis coupled to a second output node of the power converter, wherein thesecond input node is coupled to receive a second signal, and wherein theleakage cancelation current generator also receives the second signalfrom the second input node, and wherein the leakage cancelation currentgenerator generates the leakage cancelation current using the firstsignal and the second signal.
 8. The leakage current cancelation circuitof claim 7, wherein the first signal is a signal indicative of an ACvoltage between the first input node and the ground node, and whereinthe second signal is a signal indicative of an AC voltage between thesecond input node and the ground node.
 9. The leakage currentcancelation circuit of claim 1, wherein the first output node is coupledto a first input node of the power converter, and wherein the leakagecurrent cancelation circuit further comprises: a second output node thatis coupled to a second input node of the power converter; and a thirdoutput node that is coupled to a third input node of the powerconverter, wherein the leakage cancelation current generator suppliesthe leakage cancelation current onto the first output node, the secondoutput node, and the third output node via a charge injection circuit.10. A leakage current cancelation circuit that is part of an electricalpower system having a power converter, a load, and a ground node, theleakage current cancelation circuit comprising: a first input node thatreceives a first signal indicative of a common mode current from a firstnode, wherein the common mode current is present on the ground nodeduring operation of the electrical power system, and wherein the firstnode is selected from the group consisting of: an input node of thepower converter, an output node of the power converter, and a nodecoupled to the ground node; a leakage cancelation current generator thatreceives the first signal indicative of the common mode current from thefirst input node, and wherein the leakage cancelation current generatorgenerates a leakage cancelation current; a first output node, whereinthe leakage cancelation current that is generated by the leakagecancelation current generator is supplied onto the first output node,and wherein the output node is coupled to a second node selected fromthe group consisting of: an input node of the power converter, an outputnode of the power converter, and a node coupled to the ground node, andwherein the first input node is coupled to a first output node of thepower converter; and a second input node that is coupled to a secondoutput node of the power converter, wherein the second input node iscoupled to receive a second signal indicative of the common modecurrent, and wherein the leakage cancelation current generator alsoreceives the second signal indicative of the common mode current fromthe second input node, wherein the leakage cancelation current generatorgenerates the leakage cancelation current using the first signalindicative of the common mode current and the second signal indicativeof the common mode current, wherein the first signal indicative of thecommon mode current is a positive supply voltage output by the powerconverter, and wherein the second signal indicative of the common modecurrent is a negative supply voltage output by the power converter. 11.A leakage current cancelation circuit that is part of an electricalpower system having a power converter, a load, and a ground node, theleakage current cancelation circuit comprising: a first input node thatreceives a first signal indicative of a common mode current from a firstnode, wherein the common mode current is present on the ground nodeduring operation of the electrical power system, and wherein the firstnode is selected from the group consisting of: an input node of thepower converter, an output node of the power converter, and a nodecoupled to the ground node; a leakage cancelation current generator thatreceives the first signal indicative of the common mode current from thefirst input node, wherein the leakage cancelation current generatorgenerates a leakage cancelation current, and wherein the leakagecancelation current generator comprises: a current reference generatorcircuit, wherein the current reference generator circuit is coupled toreceive the first signal indicative of the common mode current and asecond signal indicative of the common mode current, and wherein thecurrent reference generator circuit generates a current referencevoltage signal; and a current controlled feedback circuit that iscoupled to receive the current reference voltage signal and generate theleakage cancelation current; and a first output node, wherein theleakage cancelation current that is generated by the leakage cancelationcurrent generator is supplied onto the first output node, and whereinthe output node is coupled to a second node selected from the groupconsisting of: an input node of the power converter, an output node ofthe power converter, and a node coupled to the ground node.
 12. A methodcomprising: (a) receiving a first signal onto a first input node of aleakage current cancelation circuit and receiving a second signal onto asecond input node of the leakage current cancelation circuit, whereinthe leakage current cancelation circuit is part of an electrical powersystem having a power converter, a load, and a ground node; and (b)generating a leakage cancelation current, wherein the leakagecancelation current is generated by performing summing anddifferentiation functions in accordance with an equation, and whereinthe equation used to generate the leakage cancelation current involvesthe first signal, the second signal, and capacitances of the electricalpower system.
 13. The method of claim 12, wherein the generating of (b)does not involve any inductor, transformer, or magnetic device.
 14. Themethod of claim 12, wherein a sum of the leakage cancelation current andthe common mode current is substantially zero under normal chargingconditions.
 15. The method of claim 12, further comprising: (c)supplying the leakage cancelation current onto at least one node of theelectrical power system such that during operation of the powerconverter a current level on the ground node is between −3.0milliamperes and +3.0 milliamperes.
 16. A method comprising: (a)receiving a first signal indicative of a common mode current onto afirst input node of a leakage current cancelation circuit and receivinga second signal indicative of the common mode current onto a secondinput node of the leakage current cancelation circuit, wherein theleakage current cancelation circuit is part of an electrical powersystem having a power converter, a load, and a ground node; (b)generating a leakage cancelation current from the first signalindicative of the common mode current and the second signal indicativeof the common mode current; and (c) supplying the leakage cancelationcurrent onto at least one node of the electrical power system such thatduring operation of the power converter a current level on the groundnode is between −3.0 milliamperes and +3.0 milliamperes, wherein thepower converter is an AC-to-DC power converter, wherein the first signalindicative of the common mode current received in (a) is received from afirst output node of the AC-to-DC power converter, wherein the secondsignal indicative of the common mode current received in (a) is receivedfrom a second output node of the AC-to-DC power converter, and whereinthe supplying of (c) involves a charge injection circuit coupled tosupply the leakage cancelation current generated in (b) onto a pluralityof input nodes of the AC-to-DC power converter.
 17. A circuit modulecomprising: a power converter that is part of an electrical power systemthat includes a load and a ground node; and means for receiving at leastone signal from a node of the power converter, and for generating aleakage cancelation current from the at least one signal, wherein theleakage cancelation current is generated without using an inductor or atransformer to sense a current.
 18. The circuit module of claim 17,wherein the means comprises an input node, a leakage cancelation currentgenerator, and an output node, wherein the input node receives the atleast one signal, wherein the leakage cancelation current generatorreceives the first signal and generates the leakage cancelation currentusing the first signal, and wherein the leakage cancelation current issupplied onto the output node.
 19. The circuit module of claim 17,wherein no inductor, transformer, or magnetic device is involved ingenerating the leakage cancelation current.
 20. The circuit module ofclaim 17, wherein under normal charging conditions, the leakagecancelation current has a sign opposite a sign of a common mode currentthat flows from the load, through a capacitance, and onto the groundnode, and wherein under normal charging conditions, the leakagecancelation current cancels the common mode current.
 21. The circuitmodule of claim 17, wherein the means is also for supplying the leakagecancelation current onto at least one node of the electrical powersystem such that during operation of the power converter a current levelon the ground node is between −3.0 milliamperes and +3.0 milliamperes.22. The circuit module of claim 17, wherein the at least one signal is asignal indicative of an AC voltage between a node of the power converterand the ground node.